1. Field of the Invention
The present invention relates to a lens driving apparatus for a disc player for optically writing or reading information to/from a disk-shaped recording medium such as a compact disc, optical disc, or the like.
2. Description of the Related Art
As shown in FIGS. 1A to 1C, hitherto, a pickup apparatus 1 for reproducing information recorded on an optical disc such as CD, DVD, or the like is known. In the pickup apparatus 1, in order to accurately read the information recorded on the optical disc, a focusing control for controlling a distance between the information recording surface of the optical disc and an objective lens is performed for a warp or oscillation of the optical disc and a tracking control for performing a tracking control of the objective lens so as to cope with an eccentricity of an information track on the optical disc is performed.
The pickup apparatus 1 comprises: a plate-shaped actuator base 4 on which a yoke 3 to which a pair of magnets 2 are fixed is arranged so as to face the actuator base 4; a movable portion 7 movably supported or connected by four supporting wires or connectors 6a to 6d to a supporting base 5 that is fixed with screws or the like (not shown) to the side surface of the actuator base 4; an actuator cover 14 in which an opening hole 13 for an objective lens 8 is formed in a top portion for protecting the movable portion 7 and which is formed in a box shape by a metal plate or resin; and a pickup body (not shown) for enclosing optical parts such as a light source, collimator lens, beam splitter, and the like.
The objective lens 8 is provided for the movable portion 7. The movable portion 7 includes: a lens holder 10 having four fixing arms 9 projecting in the tracking direction and having, for example, an almost rectangular parallelepiped shape. A focusing coil 11 wound around a body of the lens holder 10. Four D-shaped tracking coils 12 are fixed to both side surfaces of the lens holder 10 which faces the magnets 2. The four fixing arms 9 of the lens holder 10 are provided for the supporting base 5 and fixed to the four supporting wires 6a to 6d, so that the movable portion 7 is movably supported to the actuator base 4.
The four supporting wires 6a to 6d are used for movably supporting the movable portion 7 and used as connecting wires for supplying drive current to the focusing coil 11 and four tracking coils 12. For this purpose, these wires or connectors are made of an elastic member having high conductivity.
One end portion of the focusing coil 11 wound around the body of the lens holder 10 is connected to, for example, the supporting wire 6a and the other end portion is connected to the supporting wire 6b. By supplying the focusing drive currents to the two supporting wires 6a and 6b of the supporting base 5, therefore, the movable portion 7 is driven in the focusing direction.
The four tracking coils 12 fixed to both side surfaces of the lens holder 10 are serially connected by using the two supporting wires 6c and 6d and conductive wires (not shown). That is, one supporting wire 6c is connected to one end portion of each of the two tracking coils 12 which are fixed to one side surface of the lens holder 10 and serially connected. The other supporting wire 6d is connected to one end portion of each of the two tracking coils 12 which are fixed to the other side surface of the lens holder 10 and serially connected. By connecting the other end portions of the tracking coils 12 by the conductive wires, the four tracking coils 12 are serially connected to the two supporting wires 6c and 6d. Therefore, the movable portion 7 is driven in the tracking direction by supplying tracking drive currents to the two supporting wires 6c and 6d. 
The center of gravity of the lens holder 10 constructing the movable portion 7 is located almost at the center of the lens holder 10 even in a state where the focusing coil 11 is wound around the body as shown in FIG. 2A. When the objective lens 8 is built in the lens holder 10, its center of gravity is shifted to a position shown at Gn in the diagram near the top surface of the lens holder 10. The center of gravity of the tracking coils 12 fixed to both side surfaces of the lens holder 10 is located at a center position shown at Gt in the diagram of an operating line DL connecting the centers of the two tracking coils as shown in FIG. 2B. The center of gravity of the movable portion 7 in the case where the tracking coils 12 are fixed to side surfaces of the lens holder 10 is located at a position shown at Gp in FIG. 2C, namely, it is located at an upper position than the operating point of the tracking coils 12.
Although the tracking coils 12 generate a drive force around the operating point as a center, in the case where the center of gravity of the movable portion 7 is located at a position above the operating point, the movable portion 7 generates an angular moment shown at M in the diagram. In order to make the center of gravity of the movable portion 7 coincide with the operating point, hitherto, a counterweight 15 as shown in FIG. 2D is attached to the lens holder 10. That is, the generation of the angular moment is prevented by lowering the position of the center of gravity of the movable portion 7 to the position of the operating point due to a weight of the counterweight 15.
Although the counterweight 15 has an effect of suppressing the angular moment as mentioned above, there is a problem that since the total weight of the movable portion 7 is increased by the weight of the counterweight, sensitivity of the actuator is deteriorated.
The invention has been developed to solve the foregoing problems and it is an object of the invention to provide a lens driving apparatus for a disc player, in which the generation of an angular moment can be suppressed without using a counterweight and to provide printed circuit board coils for the lens driving apparatus for the disc player.
To accomplish the above object, according to a first aspect of the invention, there is provided a lens driving apparatus for a disc player having magnetic flux applying means for movably supporting a lens holder on which an objective lens, a focusing coil, and tracking coils are fixed and for applying a magnetic flux to the focusing coil and the tracking coils, wherein the focusing coil is fixed so that its center of gravity is located on the opposite side of the objective lens in the focusing direction with respect to an operating line of a tracking drive force which is generated from the tracking coils.
According to a second aspect of the lens driving apparatus for a disc player of the invention, the focusing coil and tracking coils are printed circuit board coils formed by printing coils onto a single circuit board, and the center of gravity of the printed circuit board coils is located on the opposite side of the objective lens in the focusing direction with respect to the operating line of the tracking drive force.
According to another aspect of the lens driving apparatus for a disc player of the invention, the apparatus has printed circuit board coils which are fixed to a lens holder so that parts of the coils are projected from a lower edge of the lens holder in the direction away from the objective lens in the focusing direction.
According to a further aspect of the lens driving apparatus for a disc player of the invention, the apparatus has printed circuit board coils which are formed by printing a pair of tracking coils arranged in the tracking direction on the circuit board and a focusing coil located at a position further away from the objective lens in the focusing direction than the tracking coils, and an area between the pair of tracking coils on the circuit board has a notched portion.
According to yet another aspect of the invention, there are provided printed circuit board coils for a lens driving apparatus for a disc player, in which the coils are fixed to a lens holder and at least a single focusing coil and tracking coils are printed on a circuit board, wherein the pair of tracking coils are arranged in the tracking direction and printed, the focusing coil is printed so that its center axis is located at a position different from that on a straight line connecting center axes of the pair of tracking coils, an area between the tracking coils on the circuit board having a notched portion, and the position of the center of gravity as a whole differs from that on the straight line.